Differential interference contrast (DIC) light micrograph of three species of diatoms. Stephanodiscus sp. (round), Aulacoseira granulata (long strand to the left) and Fragilaria crotonensis (right). Diatoms are a type of algae and form a significant portion of the Earth's biomass, generating about 20 to 50 per cent of the oxygen produced on the planet each year. Magnification: x425 when printed at 10 centimetres wide at its longest edge.